Download Neuromuscular control

Chapter 2
Neuromuscular Fundamentals
© 2007 McGraw-Hill Higher Education. All rights reserved.
2-1
Questions
• What dictates the amount of muscle
force created?
• Which requires more motor units; gross
movements or precision units?
• How far would you bend your knees to
do a max test for Vertical Jump?
• What occurs when NM system is
diseased? Write down some diseases
that impact the NM system.
© 2007 McGraw-Hill Higher Education. All rights reserved.
2-2
Skeletal Muscles
• Responsible for movement of body and
all of its joints
• Muscle contraction produces force that
causes joint movement
• Muscles also provide
– protection
– posture and support
– produce a major portion of total body heat
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Shape of Muscles & Fiber Arrangement
• Muscles have different shapes & fiber
arrangement
• Shape & fiber arrangement affects
– muscle’s ability to exert force
– range through which it can effectively exert
force onto the bones
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Shape of Muscles & Fiber Arrangement
• Cross section diameter
– factor in muscle’s ability to exert force
– greater cross section diameter = greater
force exertion
• Muscle’s ability to shorten
– longer muscles can shorten through a
greater range
– more effective in moving joints through
large ranges of motion
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Shape of Muscles & Fiber Arrangement
• 2 major types of fiber arrangements
– parallel & pennate
– each is further subdivided according to
shape
• Parallel muscles
– fibers arranged parallel to length of muscle
– produce a greater range of movement than
similar sized muscles with pennate
arrangement
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Fiber Arrangement - Parallel
• Categorized into following shapes
– Flat
– Fusiform
– Strap
– Radiate
– Sphincter or circular
Modified from Van De Graaff KM:
Human anatomy, ed 6, Dubuque, IA,
2002, McGraw-Hill.
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Fiber Arrangement - Pennate
• Categorized based upon the exact
arrangement between fibers & tendon
– Unipennate
– Bipennate
– Multipennate
Modified from Van De Graaff KM: Human
anatomy, ed 6, Dubuque, IA, 2002, McGraw-Hill.
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Muscle Tissue Properties
• Skeletal muscle tissue has 4 properties
related to its ability to produce force &
movement about joints
– Irritability or excitability
– Contractility
– Extensibility
– Elasticity
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Muscle Tissue Properties
• Irritability or Excitability - property of
muscle being sensitive or responsive to
chemical, electrical, or mechanical
stimuli
• Contractility - ability of muscle to
contract & develop tension or internal
force against resistance when
stimulated
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Muscle Tissue Properties
• Extensibility - ability of muscle to be
passively stretched beyond it normal
resting length
• Elasticity - ability of muscle to return to
its original length following stretching
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Muscle Terminology
• Intrinsic - pertaining usually
to muscles within or
belonging solely to body part
upon which they act
– Ex. small intrinsic muscles
found entirely within the hand
or feet
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Muscle Terminology
• Extrinsic - pertaining usually to
muscles that arise or originate
outside of (proximal to) body part
upon which they act
– Ex. forearm muscles that attach
proximally on distal humerus and
insert on fingers
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Muscle Terminology
• Action - specific movement of joint
resulting from a concentric contraction
of a muscle which crosses joint
– Ex. biceps brachii has the action of flexion
at elbow
• Actions are usually caused by a group
of muscles working together
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Muscle Terminology
• Innervation - segment of nervous
system defined as being responsible for
providing a stimulus to muscle fibers
within a specific muscle or portion of a
muscle
– A muscle may be innervated by more than
one nerve & a particular nerve may
innervate more than one muscle or portion
of a muscle
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Muscle Terminology
• Amplitude - range of muscle fiber length
between maximal & minimal
lengthening
• Gaster (belly or body)
– central, fleshy portion of the muscle that
generally increases in diameter as the
muscle contracts
– the contractile portion of muscle
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Muscle Terminology
• Tendon - Fibrous connective tissue, often
cordlike in appearance, that connects
muscles to bones and other structures
– Two muscles may share a common tendon
• Ex. Achilles tendon of gastrocnemius & soleus
muscles
– A muscle may have multiple tendons connecting it
to one or more bones
• Ex. three proximal attachments of triceps
brachii
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Muscle Terminology
• Origin
– Structurally, the proximal attachment of a
muscle or the part that attaches closest to
the midline or center of the body
– Functionally & historically, the least
movable part or attachment of the muscle
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Muscle Terminology
• Insertion
– Structurally, the distal attachment or the
part that attaches farthest from the midline
or center of the body
– Functionally & historically, the most
movable part is generally considered the
insertion
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Muscle Terminology
• When a particular muscle contracts
– it tends to pull both ends toward the gaster
– if neither of the bones to which a muscle is
attached are stabilized then both bones
move toward each other upon contraction
– more commonly one bone is more
stabilized by a variety of factors and the
less stabilized bone usually moves toward
the more stabilized bone upon contraction
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Types of muscle contraction
• Contraction - when tension is developed
in a muscle as a result of a stimulus
• Muscle “contraction” term may be
confusing, because in some contractions
the muscle does not shorten in length
• As a result, it has become increasingly
common to refer to the various types of
muscle contractions as muscle actions
instead
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Types of muscle contraction
• Muscle contractions can be used to
cause, control, or prevent joint movement
or
– to initiate or accelerate movement of a body
segment
– to slow down or decelerate movement of a
body segment
– to prevent movement of a body segment by
external forces
• All muscle contractions are either
isometric or isotonic
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Types of muscle contraction
• Isometric contraction
– tension is developed within muscle
but joint angles remain constant
– static contractions
– significant amount of tension may
be developed in muscle to maintain
joint angle in relatively static or
stable position
– may be used to prevent a body
segment from being moved by
external forces
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Types of muscle contraction
Muscle Contraction
(under tension)
Isometric
Isotonic
Concentric
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Eccentric
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Types of muscle contraction
• Isotonic contractions involve muscle
developing tension to either cause or
control joint movement
– dynamic contractions
– the varying degrees of tension in muscles
result in joint angles changing
• Isotonic contractions are either
concentric or eccentric on basis of
whether shortening or lengthening
occurs
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Types of muscle contraction
• Movement may occur at any given joint
without any muscle contraction
whatsoever
– referred to as passive
– solely due to external forces such as those
applied by another person, object, or
resistance or the force of gravity in the
presence of muscle relaxation
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Types of muscle contraction
• Concentric contractions
involve muscle developing
tension as it shortens
• Eccentric contractions involve
the muscle lengthening under
tension
Modified from Shier D, Butler J, Lewis R:
Hole’s human anatomy & physiology, ed 9,
Dubuque, IA, 2002, McGraw-Hill
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Types of muscle contraction
• Isokinetics - a type of dynamic exercise
using concentric and/or eccentric muscle
contractions
– speed (or velocity) of movement is constant
– muscular contraction (ideally maximum
contraction) occurs throughout movement
– not another type of contraction, as some
have described
– Ex. Biodex, Cybex, Lido
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Proprioception & Kinesthesis
• Taken for granted are sensations
associated with neuromuscular activity
through proprioception
• Proprioceptors - internal receptors
located in skin, joints, muscles, &
tendons which provide feedback relative
to tension, length, & contraction state of
muscle, position of body & limbs, and
movements of joints
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Proprioception & Kinesthesis
• Proprioceptors work in combination with
other sense organs to accomplish
kinesthesis
• Kinesthesis – conscious awareness of
position & movement of the body in
space
• Proprioceptors specific to muscles
– Muscles spindles
– Golgi tendon organs (GTO)
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Proprioception & Kinesthesis
• Proprioception
– Subconscious mechanism by which body is
able posture & movement by responding to
stimuli originating in proprioceptors of the
joints, tendons, muscles, & inner ear
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Proprioception & Kinesthesis
• Muscle spindles
– concentrated primarily in muscle belly
between the fibers
– sensitive to stretch & rate of stretch
– Insert into connective tissue within muscle &
run parallel with muscle fibers
– Spindle number varies depending upon level
of control needed
• Ex. Greater concentration in hands than thigh
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Proprioception & Kinesthesis
•
Muscle spindles & myotatic
or stretch reflex
1. Rapid muscle stretch occurs
2. Impulse is sent to the CNS
3. CNS activates motor neurons
of muscle and causes it to
contract
Modified from Shier D, Butler J, Lewis R: Hole’s human
anatomy & physiology, ed 9, Dubuque, IA, 2002,
McGraw-Hill.
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Proprioception & Kinesthesis
• Ex. Knee jerk or patella tendon reflex
– Reflex hammer strikes patella tendon
– Causes a quick stretch to musculotendinis
unit of quadriceps
– In response quadriceps fires & the knee
extends
• More sudden the tap, the more significant
the reflexive contraction
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Proprioception & Kinesthesis
• Stretch reflex may be utilized to facilitate
a greater response
– Ex. Quick short squat before attempting a
jump
– Quick stretch placed on muscles in the squat
enables the same muscles to generate more
force in subsequently jumping off the floor
© 2007 McGraw-Hill Higher Education. All rights reserved.
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All or None Principle
• All or None Principle - regardless of
number, individual muscle fibers within
a given motor unit will either fire &
contract maximally or not at all
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All or None Principle
• When muscle contracts, contraction
occurs at the muscle fiber level within a
particular motor unit
• Motor unit
– Single motor neuron & all muscle fibers it
innervates
– Function as a single unit
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All or None Principle
• Typical muscle contraction
– The number of motor units responding (and
number of muscle fibers contracting) within
the muscle may vary significantly from
relatively few to virtually all
– depending on the number of muscle fibers
within each activated motor unit & the
number of motor units activated
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Factors affecting muscle tension
development
• Difference between lifting a minimal vs.
maximal resistance is the number of muscle
fibers recruited
• The number of muscle fibers recruited may
be increased by
– activating those motor units containing a greater
number of muscle fibers
– activating more motor units
– increasing the frequency of motor unit activation
© 2007 McGraw-Hill Higher Education. All rights reserved.
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Factors affecting muscle tension
development
• Number of muscle fibers per motor unit
varies significantly
– From less than 10 in muscles requiring
precise and detailed such as muscles of
the eye
– To as many as a few thousand in large
muscles that perform less complex
activities such as the quadriceps
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Factors affecting muscle tension
development
• Motor unit must first receive a stimulus
via electrical signal known as an action
potential for the muscle fibers in the unit
to contract
• Subthreshold stimulus
– not strong enough to cause an action
potential
– does not result in a contraction
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Factors affecting muscle tension
development
• Threshold stimulus
– stimulus becomes strong enough to
produce an action potential in a single
motor unit axon
– all of the muscle fibers in the motor unit
contract
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Factors affecting muscle tension
development
• Submaximal stimuli
– Stimuli that are strong enough to produce
action potentials in additional motor units
• Maximal stimuli
– Stimuli that are strong enough to produce
action potentials in all motor units of a
particular muscle
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Muscle Length - Tension Relationship
• Maximal ability of a muscle to develop
tension & exert force varies depending
upon the length of the muscle during
contraction
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2-45
Muscle Length - Tension Relationship
• Generally, depending upon muscle
involved
– Greatest amount of tension can be
developed when a muscle is stretched
between 100% to 130% of its resting length
– Stretch beyond 100% to 130% of resting
length significantly decreases the amount
of force muscle can exert
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2-46
Muscle Length - Tension Relationship
• Generally, depending upon muscle
involved
– A proportional decrease in ability to
develop tension occurs as a muscle is
shortened
– When shortened to around 50% to 60% of
resting length ability to develop contractile
tension is essentially reduced to zero
© 2007 McGraw-Hill Higher Education. All rights reserved.
2-47
Muscle Length - Tension Relationship
• Ex. 1 Increasing ability to exert
force
– squat slightly to stretch the calf,
hamstrings, & quadriceps before
contracting same muscles
concentrically to jump
• Ex. 2. Reducing ability to exert
force
– isolate the gluteus maximus by
maximally shortening the hamstrings
with knee flexion
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2-48
Muscle Force – Velocity Relationship
• When muscle is contracting (concentrically or
eccentrically) the rate of length change is
significantly related to the amount of force
potential
• When contracting concentrically against a
light resistance muscle is able to contract at a
high velocity
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2-49
Muscle Force – Velocity Relationship
• As resistance increases, the maximal velocity
at which muscle is able to contract decreases
• Eventually, as load increases, the velocity
decreases to zero resulting in an isometric
contraction
• As load increases beyond muscle’s ability to
maintain an isometric contraction, the muscle
begins to lengthen resulting in an eccentric
contraction
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2-50
Muscle Force – Velocity Relationship
• Slight increases in load results in relatively
low velocity of lengthening
• As load increases further the velocity of
lengthening will increase as well
• Eventually, load may increase to point where
muscle can no longer resist, resulting in
uncontrollable lengthening or dropping of load
• Inverse relationship between concentric
velocity & force production
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2-51
Muscle Force – Velocity Relationship
• As force needed to cause movement of an
object increases the velocity of concentric
contraction decreases
• Somewhat proportional relationship between
eccentric velocity & force production
• As force needed to control an object’s
movement increases, the velocity of eccentric
lengthening increases, at least until when
control is lost
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2-52
Angle of pull
• Angle between the line of pull of the muscle &
the bone on which it inserts (angle toward the
joint)
• With every degree of joint motion, the angle
of pull changes
• Joint movements & insertion angles involve
mostly small angles of pull
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2-53
Angle of pull
• Angle of pull decreases as bone moves away
from its anatomical position through local
muscle group’s contraction
• Range of movement depends on type of joint
& bony structure
• Most muscles work at angles of pull less than
50 degrees
• Amount of muscular force needed to cause
joint movement is affected by angle of pull
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2-54
Angle of pull
• Rotary component (vertical component) component of muscular force that acts
perpendicular to long axis of bone (lever)
– When the line of muscular force is at 90
degrees to bone on which it attaches, all of
the muscular force is rotary force (100% of
force is contributing to movement)
– All of force is being used to rotate the lever
about its axis
– The closer the angle of pull to 90 degrees,
the greater the rotary component
© 2007 McGraw-Hill Higher Education. All rights reserved.
Modified from Hall SJ:
Basic biomechanics, New
York, 2003, McGraw-Hill.
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Angle of pull
• At all other degrees of the angle of pull, one
of the other two components of force are
operating in addition to rotary component
– Rotary component continues with less force, to
rotate the lever about its axis
– Second force component is the horizontal, or
nonrotary component and is either a stabilizing
component or a dislocating component, depending
on whether the angle of pull is less than or greater
than 90 degrees
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2-56
Angle of pull
• If angle is less than 90
degrees, the force is a
stabilizing force because its
pull directs the bone toward the
joint axis
• If angle is greater than 90
degrees, the force is
dislocating due to its pull
directing the bone away from
the joint axis
Modified from Hall SJ: Basic biomechanics, New
York, 2003, McGraw-Hill.
© 2007 McGraw-Hill Higher Education. All rights reserved.
2-57
Angle of pull
• Sometimes desirable to begin with the
angle of pull is at 90 degrees
– chin-up (pull-up)
– angle makes the chin-up easier because of
more advantageous angle of pull
– compensate for lack of sufficient strength
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2-58
Uniarticular, biarticular, and multiarticular
muscles
• Uniarticular muscles
– Cross & act directly only on the joint that
they cross
– Ex. Brachialis
• Can only pull humerus & ulna closer
together
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2-59
Uniarticular, biarticular, and multiarticular
muscles
• Biarticular muscles – cross & act on two
different joints
– Depending, biarticular muscles may
contract & cause motion at either one or
both of its joints
– Two advantages over uniarticular muscles
• can cause and/or control motion at more than
one joint
• are able to maintain a relatively constant length
due to "shortening" at one joint and
"lengthening" at another joint
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2-60
Uniarticular, biarticular, and multiarticular
muscles
• Muscle does not actually shorten at one
joint & lengthen at other
– The concentric shortening of the muscle to
move one joint is offset by motion of the
other joint which moves its attachment of
muscle farther away
– This maintenance of a relatively constant
length results in the muscle being able to
continue its exertion of force
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2-61
Uniarticular, biarticular, and multiarticular
muscles
• Ex.1 Hip & knee biarticular muscles
– Concurrent movement pattern occurs when
both the knee & hip extend at the same
time
– If only knee extension occurs, rectus
femoris shortens & loses tension as do
other quadriceps muscles, but its relative
length & subsequent tension may be
maintained due to its relative lengthening
at the hip joint during extension
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2-62
Uniarticular, biarticular, and multiarticular
muscles
• Ex. 2 Hip & knee biarticular muscles
– Countercurrent movement pattern occurs
in kicking
– During the lower extremity forward
movement phase the rectus femoris
concentrically contracts to flex the hip &
extend the knee
– These two movements, when combined,
increase the tension or stretch on the
hamstring muscles both at the knee & hip
© 2007 McGraw-Hill Higher Education. All rights reserved.
2-63
Uniarticular, biarticular, and multiarticular
muscles
• Multiarticular muscles act on three or
more joints due to the line of pull
between their origin & insertion crossing
multiple joints
• Principles relative to biarticular muscles
apply similarly to multiarticular muscles
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2-64
Reciprocal Inhibition or Innervation
• Antagonist muscles groups must relax &
lengthen when the agonist muscle group
contracts
– This reciprocal innervation effect occurs through
reciprocal inhibition of the antagonists
– Activation of the motor units of the agonists
causes a reciprocal neural inhibition of the motor
units of the antagonists
– This reduction in neural activity of the antagonists
allows them to subsequently lengthen under less
tension
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2-65
Reciprocal Inhibition or Innervation
• Ex. Compare the ease of
– stretching hamstrings when simultaneously
contracting the quadriceps
vs.
– stretching hamstrings without contracting
quadriceps
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Active & Passive Insufficiency
• As muscle shortens its ability to exert
force diminishes
– Active insufficiency is reached when the
muscle becomes shortened to the point
that it can not generate or maintain active
tension
– Passively insufficiency is reached when
the opposing muscle becomes stretched
to the point where it can no longer
lengthen & allow movement
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2-67
Active & Passive Insufficiency
• Easily observed in either biarticular
or multiarticular muscles when full
range of motion is attempted in all
joints crossed by the muscle
– Ex. Rectus femoris contracts
concentrically to both flex the hip &
extend the knee
– Can completely perform either action
one at a time but actively insufficient to
obtain full range at both joints
simultaneously
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2-68
Active & Passive Insufficiency
– Similarly, hamstrings can not usually
stretch enough to allow both maximal hip
flexion & maximal knee extension due
passive insufficiency
• As a result, it is virtually impossible to
actively extend the knee fully when
beginning with the hip fully flexed or
vice versa
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